ir3: Don't double-insert the first block

The first block was being added to the list twice, once here and once in
emit_block(), leading to list corruption and infinite loops when trying
to traverse the list of blocks backwards.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4658>

src/freedreno/ir3/ir3_compiler_nir.c

@@ -3262,7 +3262,6 @@ emit_instructions(struct ir3_context *ctx)
 	/* Create inputs in first block: */
 	ctx->block = get_block(ctx, nir_start_block(fxn));
 	ctx->in_block = ctx->block;
-	list_addtail(&ctx->block->node, &ctx->ir->block_list);
 
 	/* for fragment shader, the vcoord input register is used as the
 	 * base for bary.f varying fetch instrs: